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<span id="OMP_005fPLACES"></span><div class="header">
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<span id="OMP_005fPLACES-_002d_002d-Specifies-on-which-CPUs-the-threads-should-be-placed"></span><h3 class="section">4.11 <code>OMP_PLACES</code> &ndash; Specifies on which CPUs the threads should be placed</h3>
<span id="index-Environment-Variable-10"></span>
<dl compact="compact">
<dt><em>Description</em>:</dt>
<dd><p>The thread placement can be either specified using an abstract name or by an
explicit list of the places.  The abstract names <code>threads</code>, <code>cores</code>,
<code>sockets</code>, <code>ll_caches</code> and <code>numa_domains</code> can be optionally
followed by a positive number in parentheses, which denotes the how many places
shall be created.  With <code>threads</code> each place corresponds to a single
hardware thread; <code>cores</code> to a single core with the corresponding number of
hardware threads; with <code>sockets</code> the place corresponds to a single
socket; with <code>ll_caches</code> to a set of cores that shares the last level
cache on the device; and <code>numa_domains</code> to a set of cores for which their
closest memory on the device is the same memory and at a similar distance from
the cores.  The resulting placement can be shown by setting the
<code>OMP_DISPLAY_ENV</code> environment variable.
</p>
<p>Alternatively, the placement can be specified explicitly as comma-separated
list of places.  A place is specified by set of nonnegative numbers in curly
braces, denoting the hardware threads.  The curly braces can be omitted
when only a single number has been specified.  The hardware threads
belonging to a place can either be specified as comma-separated list of
nonnegative thread numbers or using an interval.  Multiple places can also be
either specified by a comma-separated list of places or by an interval.  To
specify an interval, a colon followed by the count is placed after
the hardware thread number or the place.  Optionally, the length can be
followed by a colon and the stride number &ndash; otherwise a unit stride is
assumed.  Placing an exclamation mark (<code>!</code>) directly before a curly
brace or numbers inside the curly braces (excluding intervals) will
exclude those hardware threads.
</p>
<p>For instance, the following specifies the same places list:
<code>&quot;{0,1,2}, {3,4,6}, {7,8,9}, {10,11,12}&quot;</code>;
<code>&quot;{0:3}, {3:3}, {7:3}, {10:3}&quot;</code>; and <code>&quot;{0:2}:4:3&quot;</code>.
</p>
<p>If <code>OMP_PLACES</code> and <code>GOMP_CPU_AFFINITY</code> are unset and
<code>OMP_PROC_BIND</code> is either unset or <code>false</code>, threads may be moved
between CPUs following no placement policy.
</p>
</dd>
<dt><em>See also</em>:</dt>
<dd><p><a href="OMP_005fPROC_005fBIND.html">OMP_PROC_BIND</a>, <a href="GOMP_005fCPU_005fAFFINITY.html">GOMP_CPU_AFFINITY</a>, <a href="omp_005fget_005fproc_005fbind.html">omp_get_proc_bind</a>,
<a href="OMP_005fDISPLAY_005fENV.html">OMP_DISPLAY_ENV</a>
</p>
</dd>
<dt><em>Reference</em>:</dt>
<dd><p><a href="https://www.openmp.org">OpenMP specification v4.5</a>, Section 4.5
</p></dd>
</dl>



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